Advances in our understanding of T cell activation at a molecular level have permitted the manipulation of T cell regulation in cancer patients. A newly discovered molecule involved in T cell regulation is PD-1 or Programmed Death-1, which like CTLA-4 is upregulated on activated CD4 and CD8 T cells but functions through Akt pathways to alter T cell receptor signaling in T cells. A human antibody directed against PD-1 which abrogates its function has been shown in animal tumor models to have potent anti-tumor activity alone and in combination with vaccines. In vitro experiments with melanoma patient PBMC indicated that antibody mediated PD-1 abrogation increased the generation of antigen specific T cells that were lytic, functional, gamma-interferon secreting effector cells. PD-1 antibody increased the proportion of cells that expressed CD107a, augmented avidity and caused an increase in proliferating CD8 cells after antigen exposure, promoting cell survival. PD-1 antibody could also overcome the inhibition of T cell proliferation that occurred in the presence of natural T regulatory cells. When PD-1 blockade was combined with CTLA-4 blockade in vivo in animal models there was an additive or even synergistic anti-tumor effect. When both molecules were abrogated in vitro with human melanoma specific T cells, generation of antigen specific functional T cells was markedly increased. Based on those extensive data, we propose to perform a phase I trial of escalating doses of anti-PD-1 antibody with a multi-peptide vaccine in cohorts of 10 melanoma patients each with endpoints of toxicity, definition of an MTD and comparison of immune and other surrogate assays between cohorts. After a dose of PD-1 antibody given repetitively with a vaccine that optimally stimulates immunity and is well tolerated is defined, we will perform another phase I study of the combination of PD-1 and CTLA-4 abrogating antibodies with a multi-peptide vaccine in patients with chemotherapy resistant metastatic melanoma. PUBLIC HEALTH RELEVANCE: Programmed Death-1 (PD-1) is found on the surface of immune T cells that have been activated, or "turned on", causing immune cells to decrease their function. Immune T cells that could eliminate tumors in mice have high amounts of PD-1 on their surface, so that they no longer function to kill tumor cells. Decreasing the function of PD-1 on those immune T cells by the use of antibodies in animals that have tumors has resulted in increased immunity to those tumors but also caused a reaction against normal tissues called auto-immunity. In this grant, we will perform a clinical trial in which groups of 10 patients with widespread stage IV melanoma will receive increasing amounts of the anti-PD-1 antibody with a vaccine to measure the side effects of the combination and find out how well tolerated it is. Our ultimate goal is to augment the ability of human immune cells to destroy tumor by altering the interaction of molecules that limit immunity in cancer patients like PD-1.